1. Field of the Invention
The present invention relates to hardware for fastening structural members together, for securing objects to structural members, and/or for sealing openings in structural members.
2. Description of the Related Art
FIG. 1 illustrates a prior art sealing plug 10 that may be used to fasten together a first panel 12 and a second panel 14, and to seal openings in the panels 12, 14. For example, roofs or side walls of certain structures include a plurality of sheet metal or polymeric panels that are arranged in rows. Adjacent panels can be secured to one another by forming holes in overlapping portions of the panels, and then inserting one of the plugs 10 into a pair of aligned holes in the overlapping panels. The same plug 10 may also be used to seal an opening in a single panel. As used herein the term “panel” has an expansive definition, and is not limited to structural members that have a relatively small thickness dimension and relatively large height and width dimensions.
With reference to FIG. 1, the plug 10 comprises a deformable member 16 that includes a substantially cylindrical stem 18 with a substantially disc-shaped flange 20 at a first end. The stem 18 includes a through-hole 22 that passes substantially through a center of the stem 18. The stem 18 further includes a recess 24 that is centered on the through-hole 22 and located at an end of the stem 18 opposite the flange 20. The through-hole 22 receives a shank 26 of a fastening member, such as a bolt 28. The bolt 28 is aligned with the deformable member 16 such that a head 30 thereof is positioned adjacent the flange 20. The recess 24 of the stem 18 receives a nut 32, and internal threads of the nut 32 receive the external threads of the bolt 28. One or more washers 34 may be disposed between the bolt head 30 and the flange 20.
The deformable member 16 is preferably constructed of a compressible material that has good sealing properties, such as rubber. The plug 10 is thus adapted to be inserted into an opening to seal the opening. For example, FIG. 1 illustrates the plug 10 disposed through a first opening 36 and a second opening 38 in the first and second panels 12, 14, respectively. Each of the panels 12, 14 may be sheet metal, as in the example described above. With the plug 10 disposed in the illustrated fashion, an installation professional rotates the bolt head 30, which causes the threaded portion thereof to advance through the nut 32, which in turn draws the nut 32 upward toward the bolt 28 head. As shown in FIG. 2, as the nut 32 advances the deformable member 16 is squeezed between the bolt head 30 and the nut 32. The washers 34 compress the flange 20 against the first panel 12, causing a height of the flange 20 to decrease and causing edges of the flange 20 to bulge outwardly. The nut 32 compresses the stem 18, causing the stem 18 to bulge outwardly. The bulging creates a mushroom-shaped head 40 that presses against a lower surface 42 of the second panel 14. The compression provided by the bolt 28, nut 32, washers 34 and the deformable member 16 holds the panels 12, 14 together and seals out moisture.
When a plug 10 such as the one illustrated in FIGS. 1 and 2 is used to fasten overlapping panels of sheet metal together, the sheet metal tends to expand and contract as the ambient temperature fluctuates. As the sheet metal expands, the openings 36, 38 through which the plug 10 extends become smaller and tend to cut through the relatively soft material of the deformable member 16. This interaction of the expanding and contracting sheet metal with the plug material disadvantageously shortens the lifespan of the plug 10.